1. Field of the Invention
The present invention relates to devices and methods for storing electrical energy using organic materials. More particularly, the invention relates to energy storage in a device which in part comprises organic semiconducting materials derived by modifying existing polymers or cross-linking monomers such that they are capable of functioning as electron donors or acceptors so as to form an assembly which can be repeatedly charged with and discharge electrical energy. The present invention is an improvement of the device described and claimed in U.S. Pat. No. 4,366,216 to McGinness, the disclosure of which is expressly incorporated herein by reference in its entirety.
2. Discussion of the Prior Art
Storage of electrical energy occurs through electron-transfer reactions which permit the extraction and addition of electrons through an external circuit. Various methods of storing and extracting this energy have been the focus of considerable research and development which have taken many approaches, each with individual success and compromise. Prior to the present invention, electrical energy storage systems have been devised at various levels of sophistication, each with sufficient shortcomings to render further research and development necessary.
It is known in the prior art that semiconducting materials may be employed as electron donors or acceptors. However, the operation of such devices is not fully understood and their utilization has been limited chiefly as electron acceptors (i.e. cathodes) in primary cells, primarily the halogen-organic charge transfer complexes. Moreover, the organic complex cathodes are usually coupled with inorganic anodes such as lithium. Although such batteries have high power and current characteristics and reasonably long storage life, they suffer from the disadvantages of high manufacturing cost, toxicity during manufacture and disposal, and dependence on scarce strategic materials.
A promising breakthrough in electrical energy storage has been described in the aforementioned McGinness patent which discloses the use of an oxidation-reduction polymer material, such as a polymer of quinone, semiquinone and hydroquinone units, as a storage device. The oxidation-reduction polymer when operated in the solid state was found to have extremely fast charge time (on the order of twenty times faster than ionic electrical energy storage devices) at the proper static dielectric constant while eliminating the requirements for consumable electrodes and liquid phase materials. In addition, such storage devices have extremely long lifetimes permitting, in theory, limitless charging and discharging cycles. Moreover, the oxidation-reduction polymer material storage device can be made of light weight non-toxic materials and can deliver electrical energy comparable to that of a conventional ionic battery but using a device of substantially less size and weight. The oxidation-reduction polymer materials disclosed in the McGinness patent include melanins, a polymer which is polymerized from hydroquinone and diethylamine, and others. We have found, however, that the performance characteristics of the energy storage device can be considerably improved if other oxidation-reduction polymer materials are employed or if the materials are treated in a particular manner. In particular, the energy density is improved by over two orders of magnitude.